Because there is really nothing to regulate except rates charged for electricity, fire- and building-codes, and applicable labor-laws. The code -- what miners implement to make Bitcoin possible -- cannot be hacked. Miners cannot sell a bogus product. The can't steal someone else's. But they can try to cheat the taxman. So governments will audit them, but not with the intention of shutting them down unless a government wants to monopolize mining. Doing that means a local or national government competing with international private interests, and governments aren't good at that. (That doesn't mean -- apparently like N. Korea -- that they won't try from time to time.)

Solo mining (there was some talk awhile back about regulating mining-pools as securities) is basically beyond regulation. What's needed are exchanges that are also beyond regulation. P2P buy and sell orders might be written as crowdsourced Augur bets; or initiated and completed by open-source ethereum smart-contracts that encapsulate funded debit-cards. Something that, like bitcoin mining itself, bars the kind of fraud that governments strive to protect their citizens from.

The Chinese government already has over 50% control of bitcoin mining, no need for further regulation.

The next step in their 5 year plan is to control the exchanges within their borders, which is going as planned.

What form does that 50% control take? As for the exchanges, it looks like the government is controlling them by closing them. But of course that is not permanent -- the exchanges will be back, but with licenses --- obtained by paying money under the table to important Party functionaries, no doubt.